Enbridge adds pressure restrictions for Line 5

The Michigan Department of Environmental Quality has said the spill of mineral oil used for insulation posed “no immediate public health threat,” but advised nearby towns to monitor their drinking water.(Photo: John L. Russell / Special to the Detroit News)

Enbridge Energy has placed more operating pressure restrictions on damaged pipelines across the Straits of Mackinac as a precaution, officials announced Friday.

On April 15, severe storms prompted the Canadian company to temporarily shut down Line 5, which includes twin 20-inch structures and carries about 23 million gallons of oil and liquid natural gas a day from western Canada to eastern Canada.

The Detroit News confirmed that electric transmission lines and Line 5 were dented by a ship’s anchor this month. The line was eventually restarted.

The operating pressure is what pushes the product through the line, Enbridge spokesman Ryan Duffy told The News. “Line 5 is tested at 1200 pounds per square inch, the maximum pressure we’re allowed to run at is 600 psi, but as an extra safety measure, we elect to operate the line day to day at just 150 to 200 psi.”

The restrictions are a “precautionary and prudent measure” taken in “close consultation with our federal regulator (the Pipeline and Hazardous Materials Safety Administration), with federal code, and with the State of Michigan,” Enbridge said in a statement.

Meanwhile, diver inspections continue and there are ongoing plans to reinforce the pipes. “The structural integrity of the pipes remain sound and the regular operations of the pipelines continues at the reduced pressure limit,” the company said. “We continue to work closely with the State and United States Coast Guard as they investigate the incident.”

The announcement comes a day after news emerged that a remotely operated underwater vehicle spotted damage to retired Consumers Power Co. cables while inspecting other cables owned by American Transmission Co., which released about 600 gallons of mineral oil-based insulation fluid into the Straits of Mackinac after the April 1 incident, investigators said.

Consumers, a Jackson-based utility, said its cables were laid in 1956 and retired in 1990. They do not contain the same type of free-flowing liquid that leaked from the American Transmission lines, Consumers said in a statement.

The south side of one of the two severed utility cables American Transmission owns has been soldered, capped, sealed and laid on the bottom of the Straits of Mackinac in its original position, U.S. Coast Guard officials said in a statement Friday.

“A tug, barge, and remotely operated underwater vehicle were used to permanently seal and cap the ends of the two severed ATC utility cables,” the release said. “Operations to seal and cap the remaining ends of the two severed cables will continue throughout this weekend.”

Meanwhile, the company is preparing a long-term plan to remove the damaged cables under Michigan Department of Environmental Quality oversight, the Coast Guard said. Consumers Energy is developing a similar plan.